Various techniques have been used to form ceramic materials of interest to persons of ordinary skill in the art.
It is known, for example, to utilize solid state reactions of metals with ceramics to form new ceramic phases incorporating the metal. References which utilize such an approach include: Desu et al., J. Am. Ceram. Soc., 73 (1990) 509; Gatman et al., J. Mater. Sci. Lettr. 9 (1990) 813; Morozumi et al., J. Japan Inst. Metals, 45 (1981), 184; and Choi et al., J. Mater. Sci. 25 (1990) 1957.
The pyrolysis of polymer precursors for ceramic materials is another general approach to form ceramics (e.g., the carbides, nitrides and borides). Representative references which discuss this approach for certain ceramics include: Wynne et al., Ann. Rev. Mater. Sci. (1984) 14, 297; Pouskouleli, Ceramics Intern. (1989) 15, 213; Paine et al., Chem. Rev. (1990) 90, 73; Fazen et al. Chem. Mat. (1990) 2, 96; Rees et al., J. Am. Ceram. Soc. (1988) 71, C194; and U.S. Pat. No. 4,871,826.
Certain disclosures also exist in the art for ultimately making ceramic materials utilizing a metal powder and a polymer containing a metal as at least some of the starting materials.
Japanese Patent Publication No. 54/3114 discusses the calcining of a borosiloxane polymer in a non-oxidizing atmosphere followed by its pulverization. The resulting calcined ceramic powder, rather than the starting borosiloxane polymer, is then mixed with certain transition metal elements or alloys, molded and fired in a non-oxidizing atmosphere.
U.S. Pat. No. 4,666,872 to R. H. Baney et al. teaches the use of "certain" metallic "compounds", including metallic ruthenium, palladium, silver, iridium, and platinum (which normally are considered to have a substantial degree of inertness to the formation of refractory ceramic compounds) in amounts far lower than stoichiometric (e.g., at 0.1 to 2.0 wt %) to increase the ceramic yield of a silazane polymer above the normal ceramic yield range of from about 53% to about 58% which would be realized if no metallic compound were used. This patent indicates that the metallic compound "may be added at higher levels" (Col. 4, line 62) but that "no added benefits may result" therefrom (Col. 4, line 63). Its Examples 1-7, limited to the use of compounds of the recited metals, rather than the elemental metal itself, show modest increases of ceramic yield of from about 2% to about 23%, up to a maximum of 67.5%, based on the amount of compound employed. In Example 8, which was presented for comparison purposes this patent shows that the metals of chromium, nickel, tin and zinc were ineffective in increasing the ceramic yield when utilized at the 1.0 weight percent level.
Japanese Patent Publication No. 53/52,521 describes cermet manufacture using a powder comprising one or more ceramics (e.g., oxides, carbides, nitrides, borides or silicides), a metal powder, and a semi-inorganic polymer having silicon, boron, and oxygen as the main skeleton components. This reference generally indicates that the amount of polymer used is generally in the range of from 1% to about 30% by weight of the combined amount of ceramic and metal powder. It exemplifies use of no more than 15% in one instance. It warns that use of more than 30% polymer would yield an amount of boride, carbide, oxide or their compounds, from the polymer and metal phase, which would be too high and which would cause a decrease in the strength of the product.
Japanese Patent Publication No. 57/77,083 generally advocates the impregnation or coating of a "molded" or "sintered" material with either an organic silicon polymer or a mixture of such polymer with one or more of the following: a non-oxide ceramic powder, a metal powder, or a composite powder of non-oxide ceramics and metal. In Example 4 of this reference an organic silicon polymer is dissolved in tetrahydrofuran and mixed with silicon powder, the same metal as in the polymer, and a viscous solution is formed. This viscous solution is then either used to coat a cast metal (i.e., steel) body which is heat treated (Example 5) or it is used to coat a composite sintered body formed by hot pressing a mixture of a titanium carbide powder with whiskers of metallic molybdenum (Example 6). Although this reference generally indicates that excess carbon in the polymer combines chemically with any added metal, the entire thrust of the disclosure is to heat treat a formed body after it has been coated with the polymer/metal powder composition rather than heat treatment of a composition containing the polymer and particulate metal as the main constituent reagents.